The Hajj is the world’s largest annual religious tourism event. During the Hajj approximately three to four million Muslims from around the world gather in the city of Makkah, Saudi Arabia. The Hajj is compulsory at least once in a lifetime for Muslims who are both financially and physically able to attend. Pilgrims aspire to perform the Hajj in as perfect a manner as possible to firstly, be rewarded in heaven and secondly, after returning home to obtain the title “Hajji” (for males) or “Hajja” (for females). The Hajj is highly anticipated and prepared for over many years, is performed socially and associated with norms and status, and involves hardship and sacrifice; all resulting in a memorable experience. Those returning from the Hajj generally are expected to have strengthened their Islamic beliefs. It is also expected that their increased faith will impact positively on their community, friends and family. The extant scholarly literature discusses the Hajj from an operational, economic and political perspective. This literature examines operational service issues such as the quality of accommodation and transportation, appropriate food, health-related issues and prevention from any contagious diseases, communication problems and air quality in Makkah during the Hajj. Somewhat surprisingly, given the significance of the Hajj in the spiritual development of those attending, there is little discussion of the impact of Hajj experiences on the pilgrim after returning home. The psychological impact of the Hajj pilgrimage in daily life after returning home rarely is documented in scholarly journal articles. Empirical research on personal experiences of the Hajj experience is also limited in number; mostly being exploratory and not theoretically based. In particular, there has been no quantitative study examining the relationship between the Hajj experience and an individual’s psychological or religious outcomes. To address this gap, this thesis investigates the impact of Hajj experiences on the religious commitment of pilgrims. The literature of psychological commitment and its antecedents covers numerous concepts such as goal commitment, family commitment, relationships commitment, organisational commitment, and lastly religious commitment. Recent research argues that religious commitment shares a similar psychological foundation as interpersonal relationship commitment. Thus, the relationship between individuals and their deity is considered a type of personal relationship. This study adopts as its theoretical foundation the Investment Model of Commitment, which claims that relationship commitment to a person has three antecedents; satisfaction level, quality of alternatives and investment size. This theory has been used to study intense attachments such as the romantic interpersonal relationship, commitment to an occupation, participation in sport, medical treatments and recently, religious commitment in a Christian context. In this study, the Investment Model of Commitment is applied to religious commitment in an Islamic context. The data collection for this study for the two Hajj types (regular and plus), was conducted in Indonesia which has the largest Muslim population in the world. This research applies a sequential mixed methods approach consisting of quantitative and qualitative phases. Phase one involves qualitative in-depth interviews to determine memorable components of Hajj satisfaction (both positive and negative) as well as to develop and test scales for measurement of satisfaction and religious commitment. A pilot study with 103 samples was employed to test the scales and questionnaire wording used in this quantitative data collection. The main survey involves structured questionnaires with 803 Hajji who had undertaken the Hajj within the last 3 years when this survey was conducted in 2015. The hypothesised relationships between components of the Hajj satisfaction, Hajj investment and the Islamic religious commitment were examined by using structural equation modelling. Findings revealed that there was a significant impact of Hajj satisfaction to Islamic religious commitment by using the Investment Model of Commitment with Hajj satisfaction revealed as the strongest antecedent compared to the Hajj investment, for both Hajj types. However, Hajj regular was found to have greater Islamic religious commitment after the pilgrimage compared to the Hajj plus. This thesis has made significant contributions to the body of knowledge in the literature of tourism, psychology and religious studies in the following areas: a) extending the Investment Model of Commitment (IMC) to the study of Islamic religious commitment, b) testing a modified IMC by removing the quality of alternatives concept which is not considered to apply in the context of the Hajj, c) identifying four dimensions of Islamic religious commitment instead of five as found in previous European studies—this is caused by merging the religious knowledge and religious experience dimensions and is considered to be the result of cultural differences between the German and Indonesian context—d) extending the HAJQUAL by including wait time as a measurement item, e) comparing the experiences of participants using two different Hajj pilgrimage options (regular and plus)1, f) developing an improved measurement scale for the Hajj investment and lastly, g) this is the first study to test IMC in the context of the Hajj employing mixed-methods (qualitative and quantitative). Practically, this thesis will provide guidance for Hajj organisers, the Indonesian Ministry of Religious Affairs, and Hajj tour agents handling the Hajj plus package to provide a better service for pilgrims that leads to an increase in their Islamic religious commitment. This study may benefit both individual Muslims and the Islamic community by providing a measure of the changes in level of Islamic religious commitment due to the Hajj.